The overall objective of this preclinical research project is to determine efficacy of benzyl isothiocyanate (BITC), a constituent of many edible cruciferous vegetables, for prevention of breast cancer using animal models and to determine the mechanism of its anti-carcinogenic effect using MDA-MB-231 and MCF-7 human breast cancer cells as a model. Rationale for these studies derives from recent epidemiological data and the results of our preliminary studies. Epidemiological studies have concluded that cruciferous vegetable intake is inversely associated with breast cancer risk. Our preliminary studies led us to hypothesize that BITC may delay onset and/or progression of breast cancer due to its ability to cause p53- and Cdc25C-regulated G2/M phase cell cycle arrest and caspase-mediated apoptosis involving ROS generation and Bcl-2 family proteins. This hypothesis will be tested by the following specific aims: Specific Aim 1 will determine the mechanism of BITC-mediated ROS generation, which is critical for apoptosis induction by BITC (preliminary data). Specific Aim 2 will systematically determine the role of Bcl-2 family proteins and caspases in BITC- induced apoptosis. In Specific Aim 3, experiments are designed to answer the questions whether expression of wild type p53 exacerbates BITC-mediated cell cycle arrest, and whether BITC-mediated down-modulation of Cdc25C protein is caused by redox modification of critical cysteine residue(s). Specific Aim 4 will determine the effect of dietary BITC administration on growth of MDA-MB-231 and MCF-7 xenografts in vivo in nude mice. Specific Aim 5 will determine the effect of dietary BITC administration on breast carcinogenesis using MMTV-neu transgenic mice. In Specific Aims 4 and 5, tumor tissues from control and BITC treated mice will be analyzed for apoptosis index and levels of cell cycle and apoptosis regulating proteins to gain insights into the mechanism by which BITC may inhibit mammary carcinogenesis in vivo. In summary, the proposed studies will (a) define the mechanism by which BITC inhibits growth of human breast cancer cells, which may lead to identification of mechanism-based biomarkers potentially useful in future clinical trials, and (b) determine efficacy of BITC against breast cancer in animal models, which is a prerequisite for initiation of clinical trials to determine its activity against human breast cancer.